Telephone system



May 24, 1932. 1.5.1. BOWNE TELEPHONE SYSTEM Filed NOV. 28, 1931I/QI/EA/TOR BYL. J BOWNE fikac A TTORNEV Patented May 24, 1932 UNITEDSTATES PATENT OFFICE LANGFOR-D BOWNE, OF HOWARD BEACH, NEW YORK,ASSIGNOR T'O BELL TELE- PHONE LABORATORIES,INCORPORATED, OF NEW' YORK,N. Y., A CORPORATION OF new YORK TELEPHONE svsrnm Application filedNovember 28, 1931. Serial No. 577,750.

This invention relates to. telephone systems and more particularly tothe central ofiice equipment therefor. V

It has been the usual practice in telephone systems to provide, inconnection with each subscribers line circuit terminating in a centraloflice switchboard, a line relay which operates to close a circuit to aline lamp individual to the subscribers line when a subscriber makes acall. An auxiliary or pilot relay common toa group of subscribers linesis also provided to close a circuit to a pilot signal lamp whenever acall. is made by a subscriber in that particular group. Heretofore whenefiorts have been made to dispense with the line relays by connectingthe line lamp directly to the line in order to reduce the cost of thesystem, it has been found that the combined leakage currents in a groupoi subscribersllines have been sufficient to cause operation of thepilot relay. Operation of thepilot relay by these line leakage currentsresults in the lighting of the pilot lamp and hence a false signals Anobject of the invention, therefore,'is to prevent. false operation ofthe auxiliaryor pilot relays from leakage currents in such subscribersline circuits having seriesline lamps. I

A teature .of the invention, whereby the foregoing object is attainedresides in "con necting an individualresistance element or device,having the; characteristic of decreasing in resistance inv greater thandirectproportion to: an increase: in applied potential, in. parallelwith each series line lamp and through the auxiliary or pilot relaycommon to group of lines to a source of electrical energy. Line leakageswill cause insuflicient current throu-ghfthe devices and relay inse rieswith them tooperatethe relay. .When a lamp is energizedby the-closingotits circuit, however, the potential drop across the resistance devicesbecomes great enough to cause its resistance decrease and a currentsufficient to operate the. relay results.

More specifically a resistance device whose resistance decreases ingreater than direct proportion to the applied potentialacrossitsterminals, for example, an element of thyrite,

is connected between the ungr'ounded side of each subscribers line andthe common auxiliary or pilot relay which, in turn, is connected tobattery. The resistance of these devices prevents the flow of leakagecurrents through the relay. Upon the positive grounding of a lineinresponse to the removal of the subscribers receiver from itsswitchhook', the line lamp, which is .also connected to the line, islighted. The potential drop across the: hot lamp filament is impressedacross the resistance device connected to the line and causes itsresistance to decrease to a point where the current flow. is suflicientto operate the pilot relay.

To more completely describe this invention, reference will now be madeto the drawing in which the invention is shown applied to a commonbattery manual telephone sys-- tem.

In the figure, 1, 2 and 3 represents three separate substations forminga group of substations terminating in a central ofiice switchboard 4. 5represents the cord circuit for connecting a subscribers line to anothersubscribers line in the system and 6-represents an alarm systemwhich-may be employed, for instance, as a night alarm to indicate anincoming call when a central operator is not in attendance at the board,or when there is no operator at the particular position in which thegroup of subscribers lines is located.

The operators telephone equipment and circuit associated with the cordcircuit has not been shown in the drawing because the operation andutility of such equipment is well known and the showing of suchequipment is not necessary to a ull understanding of this invention.

The subscribers line circuits 7, 8' and 9 of the substations 1, 2 and 3,respectively, terminate at the central otiice switchboard 4 in therespective jacks 10, 11 and 12. Connected directly to jack 10 is a linesignal lamp 13 connected directly to jack 11 in line signal lamp 14 andlikewise to jack 12 is connected line signal lamp 15. The line signallamps13, 14 and 15 have a filament which increases in resistance withtemperature orcurrent flow.

Tungsten filament lamps have this characteristic and may be used forthese line lamps.

Common to the group of subscribers lines represented by the substations1, 2 and 3 is pilot relay 16 which operates to close a circuit to pilotlamp 17 whenever a call comes in from a substation in the group. Toprevent operatiou of the pilot relay 16 by leak- ,age currents in thelines of the group, the

resistance devices 18, 19 and 20 are provided. The resistance devices18, 19 and 20 are connected to battery 21 through the winding of pilotrelay 16 and have the characteristic of decreasing in resistance ingreater than direct proportion to an increase in potential applied.Thyrite, for instance, has this characteristic and blocks of thismaterial I have found are adaptable for the purpose. Resistancedevice 18is connected directly to jack 10 and in shunt of line lamp 13, isconnected to battery 21 through the winding of pilot relay 16.-Resistance device 19 is connected directly to jack 11 andin shunt ofline lamp 14, is connected through the winding of pilot relay 16 tobattery 21. Resistance device 20 is connected in shunt of line lamp 15directly to jack 12 and through the winding of pilot relay 16 to battery21.

Assuming that a call is made by the subscriber at substation 1; when thesubstation loop is closed by the subscriber lifting the receiver 22 offthe book 23, the line lamp 13 at the central ofiice is lighted toindicate to the central oflice operator the incoming call. The circuitfor energization of line lamp 13 is as follows: ground, battery 21,conductor 24, line lamp, 13, conductor 25, contact 26, ring contact ofjack 10, conductor 27, left-hand side of inductance coil 28, switchhook23, transmitter 29, conductor 30, tip contact of jack 10, contact 31 toground. As the filament in the line lamp. 13 11eats up, the resistanceof the lamp increases. WVith increase in the line lamp resistance,increased potential is applied to the resistance device 18 to causeoperation of pilot relay 16. Resistance device 18', as has been saidbefore, has the characteristic of decreasing in resistance in greaterthan direct proportion to an increase in potential applied. Therefore,as the potential applied increases, the resistance intlie device 18decreases in greater than direct proportion to the increase in,potential applied. An increase incurrent flow to the pilot relay 16takes place. The circuit for energization of pilot relay 16 may betraced as follows: ground, battery 21, conductor 32, winding of pilotrelay 16, conductor 33, resistance device 18, conductor 25, contact 26,ring contact of jack 10, conductor 27, left-hand side of in ductancecoil 28, switchhook 23, transmitter 29, conductor 30, tip contact ofjack 10, contact 31 to ground.

'Pilot relay 16 upon becoming energized 3 closes a circuit to pilot lamp17 which thereupon becomes lighted to indicate to an attendant at theswitchboard an incoming call from one of the subscribers in thatparticular group.

When a central office operator answers a call by plugging into the jackof the calling line with the cord circuit 5, which in this instancewould be jack 1(), the tip and ring contacts of jack 10 are separatedfrom the contacts 26 and 31. This disconnects the line lamp 1.3 and thepilot relay 16 from the subscribers line circuit causing extinguishmentof the line lamp 13 and deenergization of the pilot relay 16 withconsequent opening of the circuit to the pilot lamp 17.

The alarm system 6 comprises an alarm signal 34, a source of energytherefor which may be, for instance, an alternating current generator 35and a switch. 36. When the alarm system 6 is to be used to indicate anincoming call, switch 36 is closed. Closing of a subscribers loopcircuit in the group served by the alarm system 6 will, in addition tocausing lighting of the line lamp, energization of the pilot relay 16andlighting of the pilot lamp 17 cause energization of the alarm relay37. The circuit for the alarm relay 37 may be traced as follows; ground,battery 38. winding of alarm relay 37, conductor 39, pilot lamp 17,conductor 40, front contact and armature of pilot relay 16 to ground.Alarm relay 37 upon becoming energized will close the circuit of thealarmsystem 6. The alarm signal 34 is operated over the followingcircuit: alternating current generator 35, conductor 41, alarm signal34, front contact and armature of alarm relay 37, conductor 42, closedswitch 36 to the generator 35.

When in answer to an incoming call the operator at the central stationplugs into the jack of the calling substation with the cord circuit 5,answering supervisory lamp 43 is lighted. The circuit for lighting ofthe answering supervisory lamp 43 may be traced as follows: ground,battery 44, conductor 45, answering supervisory lamp 43, conductor 46.resistance 47, sleeve contact 48 of the answering plug 49, sleeve 50 ofthe jack of the calling line to ground. \Vhen the answering plug 49 isfully inserted into the jack of the calling line, answering supervisoryrelay 51 becomes energized and causes shunting of the answeringsupervisory lamp 43. Answering supervisory relay 51 remains energizeduntil the calling subscriber opens the subscribers line circuit again.The circuit for energizati on of the answering supervisoryrelay 51 is asfollows: common battery 52, lower left-hand winding of repeating coilwinding of answering supervisory relay 51, ring contact of the answeringplug 49, ring contact of the jack of the calling subscribers linecircuit, through the calling subscribers loop, tip contact of the jackof the calling subscribers line circuit, tip contact of. the answeringplug 49, upper left-hand winding of the repeating coil 53, to the otherside of the common battery 52. When the answering supervisoryrelay 51 isenergized, the answering supervisory lamp 43 is shunted by way of thefront contact and armature of answering supervisory relay 51 andresistance 54. The current flow through-the lamp 43 is thereby reducedtosuch. an extent as to cause extinguishment of the lamp. Opening of, thesubscribers loop circuit will cause deenergization of answeringsupervisory relay 51 and removal of the shunt from the answeringsupervisory lamp 43' The lamp 43 will then again be. lightedto indicateto the operator at the central office that the callingsubscribers'loop-circuit has been opened and the callhasbeen'terminated. The calling end of the-cord circuit has been shownas including a calling supervisory relay 55, a calling supervisory lamp56 and the calling plug 57. A' jack 58. representing a subscribers linecircuit terminating in the central office switchboardhas. also beenincluded in the drawing. The jack 58represents the termination in thecentral oiiice switchboard of the line circuit of a called line.Insertion'of the calling plug 57 into the jack 58of the called line willresult in lighting of the calling. supervisory lamp 56. The circuit forthe calling supervisory lamp 56' is as follows: ground, battery 59,conductor .60, calling supervisory lamp 56, conductor 61, resistancev62, sleeve contact 63 of calling plug5'Z, sleeve 64 of jack58 toground.The called partyupon answering will cause closing of thecalledsubscribers loop circuit and energization of the callingsupervisory relay 55. Thecalling supervisory relay upon being energizedwill place a shunt around the calling supervisory lamp 56. When thecalled party opens the loop circuit of the called line, the callingsupervisory relay 55 will be deenergized, the shunt around the callinvsupervisory lamp will be removed and the calling supervisory lamp 56will be lighted again to indicate to the operator at the central otlicethat the called subscriber no longer desires the called connection.

The equipment at substations 2 and 3 is identical with that shown insubstation 1 and requires no further description. The resistance device19 connected through the contact 65 to the ring contact of jack 11 ofthe subscribers line circuit from substation 2 prevents leakage currentin the substatien line from affecting the pilot relay 16. Likewise theresistance block 20 which is connected through contact 66 to the ringcontact of jack 12 of the subscribers line circuit from substation 3 andthrough the winding of pilot relay 16 to the battery 21 prevents leakagecurrent in the substation line circuitfrom substation 3 from affectingthe pilot relay 16.

- If the loop circuit of substation 2 is closed, the line lamp 14 islighted. The resistance --in the line lamp 14 increases and increasedpotential is applied to the resistance device 19. The resistance in thedevice 19 decreases in greater than direct proportion to the increasedpotential applied and the current flow through the pilot relay 16increases to such an extent as to cause operation of the pilot relay 16.Pilot relay 16 in operating closes the circuit of pilot lamp 17. Thelighting of the pilot lamp 17 indicates an incoming call in the group ofsubscribers lines served by the pilot relay 16 and the lighting of theline lamp 14 indicates that the call has come in from substation 2.

A call coming in from substation 3 causes lighting of the line lamp 15,increase in the resistance in this lamp, a decrease inresistance in theresistance device 20, and opera? tion of the pilot relay 16.

The normal low resistance of each line lamp allows operation of the linelamp when a subscribcrs loop circuit served by the line lamp is'closed.The normal high resistance of each of the resistance devices 18, 19 and20 prevents operation of the pilot relay 16' by leakage current in asubscribers line circuit. Each resistance device, therefore, blocks oilfrom the pilot relay 16 any leakage current in the particularsubscribers line circuit to which the block is connected. The pilotrelay 16, therefore, cannot be operated by leakage current in anyparticular subscribers line circuit, nor by combined leakage cur rentsfrom the group of subscribers line circuits served by the pilot relay. I

WVhile elements of thyrite have been suggested for the resistancedevices 18, 19 andQO and tungsten for the filaments of the line lamps13, 14 and 15, other devices or materials having the same relativeresistance characteristics described, may be used in place thereofwithout departing from the spirit of this invention. I

What is claimed is:

1. A telephone system comprising a substation, a central station,aglinecircuit connecting said stations, a line signal connected to saidline circuit, and a source of energizing current, a relay connected tosaid source of current and said linecircuit in parallel with said linesignal, and a resistance element connected in series with said'relay toprotect the relay against operation byleak age currents'in said linecircuit. 7 2. A telephone systemcomprising a substation, a centralstation, a line circuit connecting said stations, a line signalconnected to said line circuit, and a. source of energizing current, arelay connected to said source of current and said line circuit inparallel with said line signal, and a .resistance device connected invseries Wltll'Sal'd relay to protect the relay against operation byleakage currents in said line circuit.

3. A telephone system comprising substations, a central station, linecircuits connecting the substations and the central station, a source ofenergizing current for the system, a line lamp connected to each linecircuit and said source of current, a relay common to a group ofsubstations, and a resistance element connected to each substation lineand to said source of current through said relay to protect said relayagainst operation by leakage currents in said line circuits.

4. A telephone system comprising substations, a central station, linecircuits connecting the substations and the central station, a source ofenergizing current for the system, a line lamp connected to each linecircuit and said source of current, a relay common to a group ofsubstations, and a resistance device connected to each substation lineand to'sai'd source of current through said relay to protect said relayagainst operation by leakage currents in' said line circuits. 5. Atelephone system comprising substations, a central station,line-circuits connecting the substations to the central station, asource of energy forthe system, a line lamp connected to each linecircuit and to the source of energy, a relay common to a group of linecircuits connected to the source of energy and to each line circuit-inthe group, and an element of resistance material connected to each linecircuit in the group and in series with said common relay to preventoperation of said relay by leakage currents in the line circuits, eachof said line lamps having a filament, the resistance of which increaseswith current flow to the lamp, and eachof said elements of resistancematerial having the characteristic of decreasing in resistance ingreater than direct proportion to an increase in applied potential, eachelement of resistance material being in parallel with the correspondingline lamp and permitting increase in current flow around the line lampand through said common relay when the line lamp resistance increases.

6. A telephone system comprising substations, a central station, linecircuits connecting the substations to the central station, a source ofenergy for the system, a line lamp connected to each line circuit and tothe source of energy, a relay common to a group of line circuitsconnected to the source of energy and to each line circuit in the group,and a resistance device connected to each line circuit in the group andin series with said common relay to prevent operation of said relay byleakage currents in the line circuits, each of said line lamps having afilament, the resistance of which increases withvcurrent flow to thelamp, and each of said devices having the characteristic of decreasingin resistance in greater than direct proportion to an increase inapplied potential, each device being in parallel with the correspondingline lamp and permitting increasein current flow around the line lamp 7and through said common relay when the line lamp resistance increases.

7. A telephone system comprising a group of substations, a centralstation, line circuits connecting the substations to the centralstation, a source of energy for the system, a relay common to the groupof substations connected to the source of energy and to each linecircuit in the group, a tungsten filament line lamp connected to eachline circuit and to the source of energy in shunt of said common relay,and a resistance block connected to each line circuit in parallel with acorresponding tungsten filament lamp and connected to the source ofenergy through the winding of said common relay, said resistance blockhaving the characteristic of decreasing in resistance in greater thandirect proportionto an increase in applied potential, said resistanceblock preventing operation of said common relay by leakage currents inthe lines but allowing operation of said common relay when theresistance in a line lamp increases.

8. In a telephone system including a group of line circuits, a source ofenergy for the system and a relay common to the group, an element ofresistance material connected to each line circuit and to the source ofenergy through the winding of the common relay to prevent operation ofthe common relay by leakage currents in the lines, said element ofresistance material having the character istic of decreasing inresistance in greater than direct proportion to an increase in appliedpotential and permitting operation of said common relay when a linecircuit is closed. V

In witness whereof, I hereunto subscribe my name this 25th day ofNovember, 1931.

LANGFORD J. BOWNE. M

